Comet 67P/C-G on 14 July 2014
Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
Comet 67P/C-G on 14 July 2014 - (processed view)
Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
This week's images of comet
67P/Churyumov-Gerasimenko reveal an extraordinarily irregular shape. We
had hints of that in last week's images and in the unscheduled previews
that were seen a few days ago, and in that short time it has become
clear that this is no ordinary comet. Like its name, it seems that comet
67P/C-G is in two parts.
What the spacecraft is actually seeing is the pixelated image shown at right, which was taken by Rosetta's OSIRIS narrow angle camera on 14 July from a distance of 12 000 km.
A second image and a movie show the comet after the image has been processed. The technique used, called "sub-sampling by interpolation", only acts to remove the pixelisation and make a smoother image, and it is important to note that the comet's surface features won't be as smooth as the processing implies. The surface texture has yet to be resolved simply because we are still too far away; any apparent brighter or darker regions may turn out to be false interpretations at this early stage.
But the movie, which uses a sequence of 36 interpolated images each separated by 20 minutes, certainly provides a truly stunning 360-degree preview of the overall complex shape of the comet. Regardless of surface texture, we can certainly see an irregular shaped world shining through. Indeed, some people have already likened the shape to a duck, with a distinct body and head.
Although less obvious in the 'real' image, the movie of interpolated images supports the presence of two definite components. One segment seems to be rather elongated, while the other appears more bulbous.
What the spacecraft is actually seeing is the pixelated image shown at right, which was taken by Rosetta's OSIRIS narrow angle camera on 14 July from a distance of 12 000 km.
A second image and a movie show the comet after the image has been processed. The technique used, called "sub-sampling by interpolation", only acts to remove the pixelisation and make a smoother image, and it is important to note that the comet's surface features won't be as smooth as the processing implies. The surface texture has yet to be resolved simply because we are still too far away; any apparent brighter or darker regions may turn out to be false interpretations at this early stage.
But the movie, which uses a sequence of 36 interpolated images each separated by 20 minutes, certainly provides a truly stunning 360-degree preview of the overall complex shape of the comet. Regardless of surface texture, we can certainly see an irregular shaped world shining through. Indeed, some people have already likened the shape to a duck, with a distinct body and head.
Although less obvious in the 'real' image, the movie of interpolated images supports the presence of two definite components. One segment seems to be rather elongated, while the other appears more bulbous.
Rotating view of comet 67P/C-G on 14 July 2014.
Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
Indeed, comet 8P/Tuttle is thought to be such a contact binary; radio
imaging by the ground-based Arecibo telescope in Puerto Rico in 2008
suggested that it comprises two sphere-like objects. Meanwhile, the
bone-shaped comet 103P/Hartley 2, imaged during NASA's EPOXI flyby in
2011, revealed a comet with two distinct halves separated by a smooth
region. In addition, observations of asteroid 25143 Itokawa by JAXA's
Hayabusa mission, combined with ground-based data, suggest an asteroid
comprising two sections of highly contrasting densities.
Is Rosetta en-route to rendezvous with a similar breed of comet? The
scientific rewards of studying such a comet would be high, as a number
of possibilities exist as to how they form.
One popular theory is that such an object could arise when two comets –
even two compositionally distinct comets – melded together under a low
velocity collision during the Solar System's formation billions of years
ago, when small building blocks of rocky and icy debris coalesced to
eventually create planets. Perhaps comet 67P/C-G will provide a unique
record of the physical processes of accretion.
Or maybe it is the other way around – that is, a single comet could be
tugged into a curious shape by the strong gravitational pull of a large
object like Jupiter or the Sun; after all, comets are rubble piles with
weak internal strength as directly witnessed in the fragmentation of
comet Shoemaker-Levy 9 and the subsequent impacts into Jupiter, 20 years
ago this week. Perhaps the two parts of comet 67P/C-G will one day
separate completely.
On the other hand, perhaps comet 67P/C-G may have once been a much
rounder object that became highly asymmetric thanks to ice evaporation.
This could have happened when the comet first entered the Solar System
from the Kuiper Belt, or on subsequent orbits around the Sun.
One could also speculate that the striking dichotomy of the comet's
morphology is the result of a near catastrophic impact event that ripped
out one side of the comet. Similarly, it is not unreasonable to think
that a large outburst event may have weakened one side of the comet so
much that it simply gave away, crumbling into space.
But, while the interpolated images are certainly brilliant, we need to
be closer still to see a better three-dimensional view – not to mention
to perform a spectroscopic analysis to determine the comet's composition
– in order to draw robust scientific conclusions about this exciting
comet.
Rosetta Mission Manager Fred Jansen comments: "We currently see
images that suggest a rather complex cometary shape, but there is still a
lot that we need to learn before jumping to conclusions. Not only in
terms of what this means for comet science in general, but also
regarding our planning for science observations, and the operational
aspects of the mission such as orbiting and landing.
"We will need to perform detailed analyses and modelling of the
shape of the comet to determine how best we can fly around such a
uniquely shaped body, taking into account flight control and
astrodynamics, the science requirements of the mission, and the
landing-related elements like landing site analysis and
lander-to-orbiter visibility. But, with fewer than 10 000 km to go
before the 6 August rendezvous, our open questions will soon be
answered."
Source: ESA/Rosseta
